An Afghan student of Kabul University shouted anti-US slogans during a demonstration May 10, 2009 against US-led airstrikes in the Farah province in Kabul, Afghanistan. The US military's investigation said that 26 civilians and 72 Taliban died in the incident.

Washington — A long-awaited report on a series of airstrikes in Afghanistan last month that killed a number of innocent civilians faulted American officers on the ground and in the air for failing to strictly follow the directives of their superiors.

It also questioned the use of heavy duty B-1 bombers in a mission that requires precise targeting.

At least 26 innocent Afghans were killed in three separate airstrikes by B-1 bombers assisting ground forces during a fierce fight with the Taliban, the US military's investigation into the May 4 incident in Farah Province in Afghanistan concluded.

However, the report did not dispute an independent investigation conducted by the Afghan Independent Human Rights Commission that concluded that 86 civilians were killed in the incident. Afghan officials have also said that as many as 140 civilians were killed.

"We will never be able to determine precisely how many civilian casualties resulted from this operation, but it is inconsistent with the US government's objective of providing security for the Afghan people to conduct operations that result in their death or wounding, if at all avoidable," said the report, which was released by US Central Command late Friday afternoon.

The prolonged investigation into the incident reflects the challenges of the Afghanistan mission, which has relied heavily on airstrikes that can cause many more civilian deaths, running counter to a principle objective in counterinsurgency – the protection of the local population.

The Pentagon report said that close air support – the use of planes to conduct airstrikes – should continue to be an integral part of the strategy there. But it also questioned whether B-1 bombers and the 2,000-pound munitions they carry are appropriate in fighting a counterinsurgency where precision strikes are needed.

Civilian causalities has become a major source of tension between the US and Afghan governments. Gen. David McKiernan, who was recently fired as the top commander in Afghanistan, was also credited for reducing these deaths.

The report made seven key recommendations, including increased training, better coordination with nongovernmental organizations, as well as the review of using certain aircraft such as the B-1.

Another recommendation was to improve "strategic communication," including the creation of an investigative team to respond quickly to such incidents. Some top administration officials who wanted the issue to go away resisted release of the report while others argued, ultimately successfully, that the administration should take its lumps in order to move forward.

The debate over releasing the report illustrates another problem the US faces with the Taliban continuously putting out propaganda that undermines the security mission there, experts say.

The Taliban frequently uses civilians as "human shields" by forcing them into areas where it is operating and knows the US will target. Then, the Taliban criticizes the consequent loss of civilian life to the local population. US military officials say they are unable to effectively counter this tactic because legal and bureaucratic practices prevent them from releasing detailed information until a full investigation is complete weeks later. By then, the battle of public perception – to win hearts and minds on the ground in Afghanistan - is lost.

"That has been a huge failure," says one senior military officer familiar with this case.